Floating structures, such as semi-submersible platforms, are used for offshore oil and gas drilling and production. These floating structures can work in water depths or environmental conditions that are inappropriate for other types of platforms. For example, semi-submersible platforms have been used in offshore with water depth from 80 meters to 2400 meters and in rough or mild environmental conditions. One type of floating structure is a conventional semi-submersible hull with a square ring pontoon, which typically has four columns placed at and coupled to the four corners of the pontoon. Variants of this conventional design are known.
Known designs attempt to reduce heave motion of the platform, but have shortcomings. For example, some designs are difficult to fabricate (e.g., because of complicated column shapes or overall height), or require offshore integration with topsides (e.g., because of exceeding quayside crane height and water depth limits). Some designs have an enlarged base about 50% of the draft on the bottom of each column with slim pontoons coupled between the columns to reduce vortex induced motion (VIM); such designs, however, are weak in structure, require additional material (e.g., additional hull steel), and are not cost efficient. Some designs include a column having five or six sides disposed at specific angles to each other, which typically challenges fabrication, has limited access, and is applicable only to marginal or small field developments.
Accordingly, there is a need for a floating structure that is structurally integrated and simple to fabricate, reduces environmental forces, improves platform motions (such as heave, VIM), and enhances product efficiency and competency.